Chemistry

Team solves a nearly 200-year-old challenge in polymers, allowing independent control of stiffness and stretchability

Collapsible Bottlebrush An artistic representation of a network formed by cross-linking polymers, featuring a folded backbone to which many flexible linear side chains are grafted. Credit: Liheng Cai, Baiqiang Huang/Soft Biomatter Laboratory, College of Engineering and Applied Sciences, University of Virginia

Researchers at the University of Virginia’s College of Engineering and Applied Sciences have developed a new polymer design that seems to rewrite polymer engineering textbooks. It is no longer a dogma that the harder a polymer material is, the less elastic it must be.

“We are tackling a fundamental challenge that has been considered unsolvable since the invention of vulcanized rubber in 1839,” said Liheng Cai, assistant professor of materials science and engineering and chemical engineering. .

At that time, Charles Goodyear accidentally discovered that when natural rubber is heated with sulfur, chemical crosslinks occur between the strands of rubber molecules. This cross-linking process forms a polymer network that transforms the heat-melted, flowing sticky rubber into a durable, elastic material.

Since then, it has been believed that if polymer network materials are desired to be stiff, some stretchability must be sacrificed.

That is until Tsai’s team, led by Dr. student Baiqiang Huang has proven otherwise with his new “foldable bottlebrush polymer network.” Their study, “A universal strategy for decoupling stiffness and scalability in polymer networks,” appears on the cover of the November 27 issue of Science Advances.

Polymer materials made using Tsai’s lab’s “collapsible bottle brush polymer network” can stretch 40 times more than traditional cross-linked polymer materials. Credit: Liheng Cai, Baiqiang Huang/Soft Biomatter Institute, College of Engineering and Applied Sciences, University of Virginia

“Separate” hardness and elasticity

“This limitation prevents the development of materials that require both stretchability and stiffness, forcing engineers to sacrifice one property in favor of the other,” Huang said. “Imagine, for example, a heart implant that bends with every heartbeat but lasts for years.”

Huang originally authored the paper with postdoctoral researchers Shifeng Nian and Cai.

Cross-linked polymers are used everywhere in the products we use, from car tires to home appliances, and increasingly in biomaterials and healthcare devices.

Applications the researchers envision for the material include prosthetics and medical implants, improved wearable electronics, and “muscles” in soft robotic systems that need to repeatedly flex, flex, and stretch.

Stiffness and extensibility (how far a material can stretch or expand without breaking) are related because they are derived from the same component: polymer strands connected by crosslinks. Traditionally, the way to strengthen polymer networks is to add more crosslinks.

This makes the material stiffer, but does not resolve the stiffness/stretchability trade-off. Polymer networks with more crosslinks are stiffer, but have less freedom of deformation and break easily when stretched.

“By designing a collapsible bottlebrush polymer that can store extra length within its own structure, our team is able to ‘decouple’ stiffness and extensibility, meaning that stiffness is sacrificed. “We realized that we could increase elasticity without having to do anything,” Kai said. “Our approach is different because we focus on the molecular design of network chains rather than cross-linking.”

A “tensile test” demonstrates how quickly traditional polymer networks degrade under tension. Credit: Liheng Cai, Baiqiang Huang/Soft Biomatter Institute, College of Engineering and Applied Sciences, University of Virginia

How the foldable design works

The structure of Cai resembles a bottlebrush rather than a linear polymer chain, with many flexible side chains radiating out from a central backbone.

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Importantly, the spine can fold and expand, like an accordion that expands as it stretches. When the material is stretched, hidden lengths inside the polymer are unwound, allowing it to stretch up to 40 times longer than standard polymers without weakening.

On the other hand, the side chains determine the stiffness, ultimately meaning that stiffness and stretchability can be controlled independently.

This is a “universal” strategy for polymer networks, as the components that make up the collapsible bottlebrush polymer structure are not limited to a particular chemical type.

For example, one of their designs uses polymers in the side chains that remain flexible at low temperatures. However, using side chains with other synthetic polymers commonly used in biomaterials engineering can produce gels that can mimic biological tissue.

Like many new materials developed in Cai’s lab, the collapsible bottlebrush polymer is designed to be 3D printed. This is also true when mixed with inorganic nanoparticles, which can be engineered to exhibit complex electrical, magnetic, or optical properties.

For example, conductive nanoparticles such as silver or gold nanorods, which are important for stretchable wearable electronics, can be added.

“These components provide endless options for designing materials that balance strength and stretchability while harnessing the properties of inorganic nanoparticles based on specific requirements,” Cai said. I am.

More information: Baiqiang Huang et al. A universal strategy to decouple stiffness and scalability in polymer networks, Science Advances (2024). DOI: 10.1126/sciadv.adq3080. www.science.org/doi/10.1126/sciadv.adq3080

Provided by University of Virginia

Citation: Team solves nearly 200-year-old challenge in polymers to provide independent control of stiffness and stretch (November 27, 2024) https://phys.org/news/2024-11-team Retrieved November 27, 2024 from -year-PolymerIndependentStiffness.html

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